Bio-imaging vehicles which can absorb light and facilitate fluorescent or colorimetric detection are of fundamental significance to various medical applications such as photo-thermal (W. C. W. Chan and S. Nie, Science, 1998; J. F. Lovell et al. Nat. Mater., 2011) or photo-dynamic therapy. Inorganic nanoparticles, especially quantum dots (R. Weissleder, Science, 2006) absorb light strongly and posses good luminescence properties, making them suitable vehicles for such applications domains. Yet one does not witness their widespread use in medical applications possibly because of their limited drug loading capability restricted only to the nanoparticles surface and inherent high level of toxicity. Another serious problem faced when using such inorganic nanomaterials (e.g. iodine, gadolinium, and radioisotopes) as contrasting agent9 in magnetic imaging is their unduly long residence time in the body long after the delivery procedure and higher noise to target signal ratio. To overcome these disadvantages, bio-organic nanoparticles are now being extensively used in therapeutics and for diagnostic imaging because of their much higher drug loading capacity, perfect biocompatibility and controlled activation under specific conditions such as pH, temperature etc. Biosurfactants derived from microbes are an interesting category of bio-organic systems with potential for applicability in biomedicine. They can be produced from renewable feedstock or waste material (A. Daverey et al. World Acad. Sci., Eng. Technol 2009) by a natural fermentation. Such micro-organism derived biosurfactants are also structurally very diverse. Moreover, they are readily degradable and display low toxicity. These properties are clearly desirable over those of traditional surfactants which can be eco-toxic, susceptible to bio-accumulation and generally averse to biodegradability. Some traditional surfactants with improved environmental performance such as alkyl polyglucosides, alkyl polyglucamides and fatty ester methyl ester ethoxylates are in use. However they are not necessarily made from renewable resources and may involve partial chemical processing.
A number of biosurfactants such as rhamnolipids (Pseudomonas aeruginosa), sophorolipids (Candida bombicola), trehalose lipids, cellobiose lipids, mannosylerythritol lipids, surfactin (Bacillus subtilis) and emulsan (Acinetobacter calcoaceticus) have been subjected to different scientific studies. Apart from surfactin and emulsan, all others are glycolipids which are easily the most important class of biosurfactants. Sophorolipid (J. H. Fuhrhop and T. Wang, Chem. Rev., 2004) are amphiphilic molecules which contain both hydrophobic (nonpolar) and hydrophilic (polar) groups. This character enables them to reduce the surface and interfacial energies leading to formation of emulsions. The foremost reasons for a high and increasing level of interest in Sophorolipid is due to their biodegradability and low toxicity as well as their unique structures that can facilitate their engineering to suit a specific application domain. Also, sophorolipids are easily synthesized by non-pathogenic yeast using very cost effective resources.
When dissolved in water, Sophorolipid molecules can form micelles-like structures. Some literature reports also discuss supramolecular assemblies of Sophorolipid monolayer vesicles, helical fibers/ribbons/tubules, and even rigid rods.
In current biomedical scenario optically active nanomaterials hold great promise in the context of advancement of a range of biophotonic and photocoustic techniques via nanoscale optical effects and synergistic integration of multiple imaging and therapeutics. Towards this end fluorescent nanoparticles are of immense significance because they facilitate multiple bio-imaging and therapeutic modulations. Inorganic nanomaterials such as quantum dots with intrinsic fluorescence properties have several disadvantages for such applications including toxicity. A cursory review of prior art indicates that despite the availability and unique characters of Sophorolipid, the applications of the same is not scaled for biomedical applications such as imaging.
Therefore, there is a need in the art to provide sophorolipid based mesoscale and biocompatible molecular self-assembled structures that show remarkable fluorescence that can be scaled for biomedical applications.